Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

[sberri]

my samsung pn50b860 shut off during an all day movie marathon last week. No standby led, no picture, no sound, no "clicking noises".....it was completely dead. I removed the back and discovered the two fuses on the A/C input side of the power board (part# bn44-00277a) were blown. I performed a visual inspection for bad capacitors as well as any other obviously bad components and everything looked okay. After replacing the bad fuses with identically rated ceramic fuses, I plugged the TV in. It attempted to power itself on and immediately blew both fuses again. Just for giggles, I repeated the process and witnessed the same results. I find it odd that it blows the fuses on both legs of the A\C input. Could that be a clue as to with components on the power board might be bad? I greatly appreciate any and all help.

Thank you in advance for your insight,

Scott Berri

[Alastair E]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

Check ALL the MOSFETS on the heatsinks as well as the bridge-rectifier for short-circuits...

There's obviously a very heavy short there to blow both mains-fuses like that...

[sberri]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

Thank you for the quick response. Is it best to remove them from the board to test them?

[tom66]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

You can test in circuit for now, but if you find a shorted one remove it and test out of circuit to be sure.

[budm]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

Good clear pictures of your board will also be a big help.

[tom66]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

Schematic if it helps:

[sberri]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

I finally got the time to test the power board. After finding two bad MOSFETs, I decided to just swap out the board. I adjusted the VS and VA voltages as per the sticker inside the TV. The picture looks great for about five minutes and then becomes awful. I've attached images showing the screen. I also noticed the va an vs voltages drop after the TV is on for a few minutes . Not sure if this is normal behavior

[tom66]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

Dropping Vs will cause this fault, and it's not normal for Vs to drop.
Does the picture get better if only a dim image is displayed? (For example, only the "No Signal" box)

[Alastair E]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

Hmm--Thats a shame. Looks like the new PSU is faulty if both Va and Vs are dropping like that. Can you return it to where you bought it?
They should be stable to within a volt or so--no matter what happens while the sets running....

[sberri]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

The picture does get better at the no signal screen. It looks like a normal no signal screen. As soon as I feed it a signal, it gets bad again.

[sberri]

Re: Samsung pn50b860y2f plasma TV blows A/C line in fuses on power board bn44-00277a

It's taken a while for me to get and install new X, Y, and their buffer boards. Picture is great until tv has warmed up (30 minutes or so). If I open a menu from any source I get a ghost of the menu after exiting. Picture looks fine other than the ghost image of static menu. Any ideas?